FIELD OF THE INVENTION
The present invention relates to an improved process for the ozonization of .alpha.,.beta.-unsaturated cyclohexanones whereby 5-ketoalkanoic acids are obtained in good yield.
DESCRIPTION OF THE PRIOR ART
Various oxidative procedures for the preparation of keto acids from dione cyclics are described in British patent application GB No. 2083035A published May 17, 1982. The British application is primarily concerned with methods for oxidatively cleaving isophorone to obtain 5-keto-3,3,-dimethylhexanoic acid which is the precursor of dimedone (1,1-dimethyl-3,5-diketocyclohexane)--a compound useful as a reagent for the detection of ethyl alcohol and the identification of aldehydes and for other industrial applications.
In addition to the conventional catalytic oxidation procedure described in the British application, wherein isophorone is oxidized using sodium periodate or sodium hypochlorite in the presence of ruthenium oxide catalyst, the use of ozone is also disclosed for the preparation of 5-keto-3,3-dimethylhexanoic acid. In one procedure ozone is reacted with isophorone in methanol and, upon completion of the ozonolysis, the resulting ozonized mixture decomposed by heating at 50.degree.-60.degree. C. for three hours with nitric acid. Heating ozonized mixtures at elevated temperatures in the presence of oxidizing agents and an organic solvent having a low flashpoint, is not, however, recommended for the large-scale preparation of 5-keto-3,3-dimethylhexanoic acid in view of the recognized thermal instability and reports of spontaneous decomposition of ozonized mixtures.
The ozonolysis of the .alpha.,.beta.-unsaturated cyclic ketone is therefor carried out in a two-phase mixture of an aqueous phase and an organic solvent phase in the presence of an alkali metal hydroperoxide and a phase transfer catalyst. While this method makes it possible to conduct the reaction at much lower temperatures, the process still requires the use of a strong oxidizing agent (hydroperoxide) with the ozone and the use of expensive and highly toxic organic solvents (chloroform or methylene chloride). Furthermore, the bi-phase systems require the use of a phase transfer catalyst in order to accomplish the reaction.
It would be highly desirable if a process were available whereby .alpha.,.beta.-unsaturated cyclic ketones, such as isophorone, could be efficiently and safely ozonized to the corresponding keto acids. It would be particularly advantageous if such a process did not require the use of strong mineral acids, peroxides or hydroperoxides for the ozonization or decomposition or the use of flammable or otherwise potentially hazardous organic solvents. The process would be even more desirable if the presence of a phase transfer catalyst was not required.